If the sound is fine when you are watching TV or playing music using Bluetooth, we recommend you try the following:
Delete the Google Home app from your phone or tablet.
Reset your HK Surround
To restore the factory default settings, select ‘Options’ > ‘Factory Reset’ on the display. All settings will be deleted and you will now be ready to reconfigure your product in the Google Home app.
Then reinstall the Google Home app and preferably run the setup when your phone/tablet is connected to the faster 5 GHz home WiFi network.
If you have a standard provider router with a 2.4 GHz and 5 GHz home WiFi network, we recommend that you separate these two bands by giving the 2.4 GHz and 5 GHz networks each a separate SSID (network name) and password.
To do this, you must log into the modem. If you are not sure how to do this, we recommend you contact your Internet provider, who will be able to assist you with this over the phone.
In the network section there's an article witch explains how this can be done manually. Afterwards, be sure to connect the phone or tablet to the faster 5 GHz home WiFi network before you run the setup again. If you have made changes to your network settings, make sure that all your devices are registered on the ‘new’ network and make sure to forget any other networks with which your phone/tablet was configured to connect automatically.
Also please check out the article about preventing interference. If you are unable to easily maintain the wireless connection, the HK Surround set can also be connected directly to the network with an Ethernet cable.